UK: An unsettled week with occasional bands of rain and some sunny periods. Air from the south and southwest gave milder temperatures and a hint of the beginning of spring.
Falklands: A relatively settled week, generally fine and dry with mist forming in places overnight as high pressure built to the north.
Ascension: After a fairly dry start to the month we’ve finally been getting a few more showers in this last week. Our record temperature at the airhead has been broken again with a max of 32.5C on Thursday.
St. Helena: A showery week, and particularly damp on Thursday with more frequent showers, giving 17.2mm
Somewhere over the rainbow…
I saw a lovely rainbow yesterday morning, the first I’ve seen since arriving over a month ago. It has been very dry over the last month and obviously no rain = no rainbow! but we have started to begin to get a few more showers recently. Rainbows are only visible on Ascension early in the morning or late in the afternoon because the sun rises high in the sky quickly. As rainbows are centred exactly opposite to the Sun, during most of the day they would be below the horizon and so not visible.
The colours are formed when light is first refracted when it enters the raindrop and then reflected off the back of the raindrop and then refracted again as it leaves back towards the sun. A bow's appearance depends on drop size. The best are narrow ones with intense colours and these are made by large drops several millimetres in diameter, which fall from a moderate or heavy shower. Smaller drops produce broader bows with less saturated colours. Very small drops give nearly colourless cloudbows and even white fogbows. Sea spray can also give rainbows, but as the density of seawater is different from rainwater it will create a rainbow with a smaller radius than a true rainbow.
If you look closely the sky inside the rainbow is slightly brighter than that outside, because as well as creating the colourful rings the raindrops also direct more light there too.
It is also possible to get a moon-bow, although these are weak and very rare!
Compiled by Rainbow Bright
Crown Copyright 2010
Met Office Ascension Island base